I have produced this web site to provide contemporary and up to date reliable information on conditions which affect the heart. The management of many heart conditions has advanced considerably in recent years. It provides information about who I am, but is a reference site to collate and organise information relevant to my work. Others may find this useful.

About Me

Mark Dayer was appointed as a consultant cardiologist at Somerset Foundation Trust in 2007 and also practiced at The Nuffield Hospital Taunton. At Somerset Foundation Trust he was at various times the lead for heart failure, devices, and the clinical lead for the service. Before leaving, he was the lead for adult congenital heart disease and the Clinical Director for Medicine. He was also the domain lead for Device Therapy and Arrhythmias at the National Institute for Cardiovascular Outcomes Research. In January he became an Honorary Associate Professor at Plymouth University. He has now left the UK to take up a post as lead for heart failure at the Mater Private Hospital in Dublin.


He trained at Guy’s and St Thomas’ Hospitals graduating in 1995 with honours in Medicine and a first-class honours degree in Psychology. He became a Member of the Royal College of Physicians in 1998 and a Fellow in 2011. He was awarded a PhD from Imperial College in 2008, focusing on exercise limitation in heart failure. He gained his Certificate of Specialist Training in Cardiology and General Internal Medicine in February 2008. In 2007 he became a Certified Cardiac Device Specialist and in 2013 obtained Level II Cardiac CT Accreditation. 


His principal clinical interests are:


  1. Cardiac implantable electronic devices (pacemakers, defibrillators and cardiac resynchronisation therapy)
  2. Infective endocarditis
  3. Arrhythmias and syncope
  4. Inherited Cardiac Conditions
  5. Adult Congenital Heart Disease
  6. Cardiac CT scanning
  7. Sports Cardiology


The main focus of his research has been Infective Endocarditis. He is currently ranked in the top 10 in the world (by publications) in this field and lectures nationally and internationally on the subject. He has published over 100 peer-reviewed articles in medical journals. 


He enjoys endurance exercise in his spare time and has completed Triathlons up to and including Ironman distances, multiple marathons (including Ultras) and endurance open-water swims. He provides medical advice to the website Crickles (https://crickles.casa), and occasionally contributes to articles in Cycling Weekly. Kness are a recurrent issue, however.


The photo is by Tony Wright, one of our local GPs.

ISABEL - An online symptom checker

ISABEL is an online symptom checker. If you have symptoms and are concerned about what might be causing them, you could visit this website and type in your symptoms. It can suggest what may be wrong with you.


It's impossible for doctors to know about every possible diagnosis - ISABEL is a service I use in more difficult cases to help me get the correct diagnosis. I think it's the best one currently available.